Eating little may help people live longer, a study has found, of­fer­ing sup­port for an idea that has tan­ta­lized sci­en­tists for dec­ades.

Re­search­ers have long known that cut­ting an­i­mals’ food supply to near-starva­t­ion lev­els gives them—for rea­sons still un­clear—long­er lives and health­i­er old age. Stud­ies have found that in hu­mans, too, sharply re­duced eat­ing is as­so­ci­at­ed with health­i­er ag­ing, as long as nu­tri­tion­al ba­lance is main­tained.

But wheth­er this prac­tice could ac­tu­ally length­en our lives has re­mained un­cer­tain.

Some sci­en­tists have ar­gued that it’s doubt­ful, be­cause hu­mans al­ready live un­usu­ally long. Only one small past study in hu­mans of­fered weak ev­i­dence that peo­ple eat­ing less lived long­er, ac­cord­ing to its au­thors, who were al­so in­volved in the new re­search.

The new study is the first to probe the claim by com­par­ing hu­man popula­t­ions, wrote the Amer­i­can and Jap­a­nese sci­en­tists in a re­port on their find­ings.

More­o­ver, they added, it’s “the first study that has shown ex­tend­ed av­er­age and max­i­mum life span in a hu­man popula­t­ion that is po­ten­tially due to” re­duced eat­ing. The prac­tice is known as ca­lor­ic re­stric­tion.

The re­search­ers stud­ied res­i­dents of the Jap­a­nese is­land of Ok­i­nawa, known through much of the last cent­ury both for ex­cep­tion­ally long-lived in­hab­i­tants and for very spare, though bal­anced di­et­s. The in­vest­i­gat­ors said they found ev­i­dence that the two things are at least par­tially re­lat­ed.

Al­though that con­clu­sion might seem ob­vi­ous to some—given the past re­search—the sci­en­tists wrote that to reach it, they had to ac­count for some fac­tors that had ham­pered sys­tem­at­ic anal­y­sis. For one, Oki­na­wan di­ets have changed, be­com­ing richer since about the end of the 1960s. Al­so, it was­n’t clear how to best as­sess his­tor­i­cal di­e­tary in­take and com­pare it to that of oth­er popula­t­ions.

The find­ings, by Brad­ley Will­cox of the Pa­cif­ic Health Re­search In­sti­tute and John A. Burns School of Med­i­cine in Hon­o­lu­lu and col­leagues, ap­pear in the No­vem­ber is­sue of the re­search jour­nal An­nals of the New York Acad­e­my of Sci­ences.

An­i­mal tests have found that the ex­treme di­et­ing of ca­lor­ic re­stric­tion en­tails cut­ting some 40 per­cent of calo­ries to get the strongest life-extending ef­fects. An­i­mals placed on such reg­i­mens live up to 40 per­cent long­er than nor­mal, as long as the di­et re­mains nu­tri­tionally bal­anced. (Some sci­en­tists pro­pose—a­gain based mostly on an­i­mal test­s—that tak­ing a sub­stance called res­ver­a­trol may rep­li­ca­te ca­lor­ic re­stric­tion’s ben­e­fits, with­out the un­pleas­ant­ness.)

Will­cox and col­leagues found that at least from the mid-20th cen­tu­ry through the 1960s, the Oki­na­wan di­et was about 11 per­cent short of what would nor­mally be rec­om­mended to main­tain body weight. As of 1995, the av­er­age Oki­na­wan lived about five years long­er than the av­er­age Amer­i­can, and about 18 months more than the av­er­age Jap­a­nese.

The is­landers’ spar­tan di­ets may have been a leg­a­cy of “pe­ri­odic crop fail­ures that oc­curred in Oki­na­wa in the early 20th cen­tu­ry and a long his­to­ry of mar­gin­al food sup­ply,” the re­search­ers wrote.

The study had some weak­nesses, they added; for in­stance, it could­n’t rule out that Oki­na­wans lived long­er be­cause of the types of nu­tri­ents they ate, rath­er than the amount. None­the­less, the “ten­ta­tive” find­ings fit with a broad ar­ray of an­i­mal stud­ies, and point to a need for still more re­search, Will­cox and col­leagues wrote.